Seven South Sudanese politicians face charges of treason over an alleged coup attempt in December that sparked weeks of fighting, the authorities have said.

Eleven officials were arrested at the time and the rebel side has made their release a condition of any peace deal to follow last week's ceasefire.

Those to be tried include three people not in custody, including ex-Vice-President Riek Machar.

Seven of the other detainees have been released to the authorities in Kenya.

Analysis

By James CopnallSouth Sudan analyst

This release of several of the detainees will probably not remove an obstacle to the negotiations. The rebels want all of the men released - and so do the US and other countries mediating in this crisis. The idea is that all these heavyweight figures should take part in talks on resolving the political crisis that triggered this conflict.

Outside South Sudan, at least, President Salva Kiir has not been able to convince many people that his former deputy Riek Machar and the remaining detainees were involved in an attempted coup.

The families of the prisoners say they are concerned about their safety. Attention now focuses on President Kiir, who has hinted that after a trial the men could receive an amnesty.

However, it is difficult to see how court proceedings could be completed before the restart date for negotiations, in early February. That could force a delay.

They have appeared at a news conference with Kenyan President Uhuru Kenyatta in the capital, Nairobi.

Correspondents say the treason charges, announced by South Sudan's Justice Minister Paulino Wanawila, could jeopardise the ceasefire deal.

The government had previously indicated that it might grant an amnesty the detainees, who are prominent political figures from a faction of the governing SPLM party.

It underscores the animosity between the government of President Salva Kiir and the rebels, many of whom are loyal to Mr Machar.

Although both men have supporters from across South Sudan's ethnic divides, fighting has often been communal, with rebels targeting members of Mr Kiir's Dinka ethnic group and government soldiers attacking Nuers.

Mr Kiir accused Mr Machar and other former officials of attempting a coup after fighting broke out in the capital Juba on 15 December, something Mr Machar denies.

'Not bitter'

Mr Wanawila said treason charges would be brought against four men who were already in custody, plus three men on the run.

"If someone violates the law you don't go and torture that person, you prosecute that person according to the law," he said.

The seven men targeted for trial include:

Riek Machar, whose sacking in July as Mr Kiir's deputy sparked much of the unrest

Pagan Amum, former secretary general of the ruling party

Former National Security Minister Oyai Deng Ajak

Former ambassador to the US Ezekiel Lol Gatkuoth

Chief rebel delegate Taban Deng, who signed the ceasefire.

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The ceasefire was agreed last Thursday after talks in Ethiopia

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UN aid chief Valerie Amos visited one of several UN warehouses from which a total of 3,700 tonnes of food was stolen

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More than 645,000 people have been displaced by the conflict

One of the detainees released in Kenya, former South Sudan Justice Minister John Luke, said they wanted to work with mediators to quickly resolve the crisis.

"We don't feel bitter, we don't feel that the president is our enemy... we are all feeling sad about the tragic situation," he said at the news conference.

Both sides say they are committed to the ceasefire, but there is still fighting in some areas, and the United Nations has described the situation as "fragile".

Aid groups say up to 10,000 people have been killed in the conflict.

The UN says more than 646,000 people have been displaced inside South Sudan and more than 123,400 people have fled to neighbouring countries.

The UN's aid chief Valerie Amos has wrapped up a three-day visit to the country with a trip to Malakal, where she said some people were afraid to return home despite the truce.

Baroness Amos said the people she spoke to said they had "completely lost faith'' and wanted to be relocated to other parts of South Sudan, or even out of the country.

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Fighting erupted in the South Sudan capital, Juba, in mid-December. It followed a political power struggle between President Salva Kiir and his ex-deputy Riek Machar. The squabble has taken on an ethnic dimension as politicians' political bases are often ethnic.

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Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam.

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Both Sudan and the South are reliant on oil revenue, which accounts for 98% of South Sudan's budget. They have fiercely disagreed over how to divide the oil wealth of the former united state - at one time production was shutdown for more than a year. Some 75% of the oil lies in the South but all the pipelines run north.

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The two Sudans are very different geographically. The great divide is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. South Sudan is covered by green swathes of grassland, swamps and tropical forest.

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After gaining independence in 2011, South Sudan is the world's newest country - and one of its poorest. Figures from 2010 show some 69% of households now have access to clean water - up from 48% in 2006. However, just 2% of households have water on the premises.

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Just 29% of children attend primary school in South Sudan - however this is also an improvement on the 16% recorded in 2006. About 32% of primary-age boys attend, while just 25% of girls do. Overall, 64% of children who begin primary school reach the last grade.

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Almost 28% of children under the age of five in South Sudan are moderately or severely underweight - this compares with the 33% recorded in 2006. Unity state has the highest proportion of children suffering malnourishment (46%), while Central Equatoria has the lowest (17%).